| Ultrasonic solidification technology is a new method to refine the solidification structure and improve the performance of the metal melt by applying ultrasonic wave in the liquid metal solidification process. The traditional method of ultrasonic wave guide is to insert the ultrasonic wave guide rod directly into the liquid metal. But for iron and steel materials, the processing temperature is generally above 1600?, it is difficult to find a suitable material. This has affected the application of ultrasonic wave in steel and iron materials. In order to solve this problem, this paper introduces the design of non contact ultrasonic leading in device, namely ultrasound is introduced in the side or at the bottom of the ingot mould to observe the influence on the quality of ingot solidification.In this paper, we first used the method of water simulation experiment to study the effect of ultrasonic side import on the flow field in mold. On this basis, the thermal simulation experiment was carried out. And taking GCr15, 9Cr2Mo as the research object, discusses the effect of ultrasonic on solidification structure of steel and segregation of elements from the side and the bottom of the ingot mould, and has obtained the following research results.(1) Water model experiment show as follow: without the treatment of ultrasonic, the uniformity of the flow field in the transverse direction and the longitudinal direction is poor. With the increasing of power, the flow field spreads to the model in the horizontal and vertical direction steadily and the relative depth first increases and then decreases at the center of the flow field. The flow field of ultrasonic power 400 W is significantly improved when compared with 300 W. The relative depth of the flow field is 0.56 under the treatment of ultrasonic power 500 W. And the flow field is more uniform in both longitudinal and transverse direction. When the ultrasonic powers are 700 W and 1000 W, the relative depth of the flow field are 0.46 and 0.45 respectively. The depth of the flow field is shallow. Inclusions in the mold don't have enough time to rise to the surface. At the same time, it can also cause the liquid level fluctuation, and even cause the rolling slag.(2) The ultrasonic was imported to the side of the mold wall during solidification of GCr15 steel. It is found that ultrasonic wave can significantly improve the solidification structure of molten steel, eliminate coarse columnar grain, grain refinement and uniform structure. The ultrasonic treatment effect is different when adding to different ultrasonic power. With the increasement of ultrasonic power, the effect of the optimization on the grain size and microstructure is more obvious. Ultrasonic power varying from 300 to 500 W, the treatment effect of liquid steel is optimal, while ultrasonic power is more than 500 W, the effect of ultrasonic treatment becomes poor. Ultrasonic treatment can effectively inhibit the segregation of Si, C, Mn elements from GCr15 bearing steel, diffrently from the Cr element. After ultrasonic treatment, the size of carbide in GCr15 steel can be remarkably refined and uniform distribution of carbide by the function of nonlinear ultrasonic. When the ultrasonic power is 300 W, the carbide distribution is uniform, the carbide size is 2.96?m.(3) For 9Cr2Mo steel, a method were designed that ultrasonic were imported from the crystallizer side and bottom respectively in electro slag remelting process, which shows as follow: After ultrasonic treatment, the segregation degree of each element in the steel reduced, the uniformity increased, and the density increased. Under the same power, the improvement of each element distribution is different. That is, the sensitivity of different elements to ultrasonic power is different. Si and C elements in the ultrasonic 500 W segregation degree is smaller and uniform degree is bigger, and the Mn element in ultrasonic 300 W segregation degree is smaller and the uniformity is bigger, the Cr element in the 700 W segregation degree is smaller and the uniformity is bigger. Combined with the analysis of density under ultrasonic power 500 W, each element relatively evenly distributes, the segregation degree is relatively small, and the uniformity is larger, the density is the highest.(4) In the process of electro slag remelting, 9Cr2Mo alloy tool steel was treated with different power ultrasonic imported from bottom. In the appropriate ultrasonic power, Si, Mn,, Cr, C, the degree of segregation of the steel reduces, the uniformity and the density increases, the distribution of elements tend to be uniform. when the power is 500 W, each element segregation degree is minimum, uniformity and maximum density. The distribution of the elements in the solidification structure is the most uniform. The minimum segregation degrees of C, Si, Mn, Cr are respectively 0.0596, 0.025, 0.0464 and 0.0373, uniformity degree respectively 0.9261, 0.9793, 6 and 0.6334, and maximum density is 0.968.(5) Research results show that, treating liquid steel with ultrasonic "non contact" method, a suitable power ultrasonic treatment is helpful to improve the solidification of the ingot and refine the grain. At the same time, the main element segregation of the steel is decreased, and the distribution of solute elements becomes uniform. |
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